What happened
Shortly after takeoff, as the aircraft climbed through 3,100 feet, the No. 1 engine fire warning activated. Approximately 20 seconds later, the captain moved the No. 1 throttle to idle and instructed the first officer to declare an emergency with air traffic control. About 47 seconds after the initial warning, the captain directed the first officer to begin the engine fire emergency procedures checklist.
About 88 seconds after the fire warning first activated, the engine fire warning system deactivated due to fire damage affecting one of the two fire loops. This occurred two seconds before the first officer moved the No. 1 fuel lever to the off position, which shut down the No. 1 engine. The flight crew did not observe the warning indicating that the No. 1 fire loop system was inoperative. Because the fire light had extinguished, the crew elected to stop the emergency procedure and did not activate the No. 1 fire handle. Consequently, pressurized fuel continued to supply the engine, feeding the fire.
The flight crew returned to the departure airport. During the descent, at approximately 2,000 feet and three minutes before landing, a flight attendant reported that a mechanic on board observed the No. 1 engine was still smoking or on fire. The crew took no further action and landed the aircraft. One minute after stopping, the captain ordered an emergency evacuation, instructing passengers not to use the left overwing exits. Approximately 1 minute and 55 seconds after landing, the crew pulled the engine and auxiliary power unit fire handles and discharged the fire bottles into the No. 1 engine.
The investigation
Post-incident examination of the No. 1 engine revealed that all the accessory gearbox idler adapter attachment bolt inserts had backed out. This allowed fuel lines to unseat, spraying pressurized fuel onto hot engine components and causing ignition. It was determined that during an engine overhaul at a vendor's facility on September 26, 1995, the accessory gearbox idler adapter had been reworked according to General Electric Aircraft Engine Service Bulletin 72-743; however, smaller-than-required adapter bolt inserts had been installed.